The major obstacle in cancer chemotherapy is the development of drug resistance in tumor cells. The biochemical and molecular mechanisms associated with multidrug resistance (MDR) are know to be diverse. The major changes are (a) over expression of MDR gene associated with drug efflux pump plasma membrane glycoprotein 170 (gp 170), (b) decreased generation of cytotoxic drug moiety and (c) increased mechanisms for drug detoxification. We found the major changes in our independently selected adriamycin resistant human breast cancer MCF-7 cans are the over expression of gp 170 and decreased glucose-6-phosphate dehydrogenase activity in early, intermediary and late stages of resistance.